Low-Salt Diet Cut BP by 6 mm Hg in 1 Week: CARDIA-SSBP

People who followed a low-salt diet for just a week experienced a reduction in systolic blood pressure of about 6 mm Hg, in a new study.

The CARDIA-SSBP trial involved 213 individuals aged 50-75 years, including those with and those without hypertension, and showed that the decline in blood pressure brought about by a low-salt diet was independent of hypertension status and antihypertensive medication use. It was also generally consistent across subgroups and did not result in excess adverse events.

“The blood pressure reduction we see here is meaningful, and comparable to that produced by one antihypertensive medication,” lead investigator, Deepak Gupta, MD, Vanderbilt University Medical Center, Nashville, Tennessee, told theheart.org | Medscape Cardiology.

Gupta presented the CARDIA-SSBP study on November 11 at the American Heart Association (AHA) Scientific Sessions 2023, held in Philadelphia. The study was also published online on November 11 in JAMA. The exact menus used in the study are available in a supplement to the JAMA paper.

“In order to live a healthy lifestyle, understanding what we eat has important health effects. Raised blood pressure contributes to 1 out of every 8 deaths worldwide,” Gupta noted. “If people want to lower their blood pressure, attention to dietary sodium is one part of that. If individuals can stick with a low sodium diet, they may be able to stop taking one of their antihypertensive medications, and those who are normotensive will be less likely to develop hypertension.”

Commentators said the study had significant implications for public health, but they pointed out that maintaining a low-sodium diet over the long term is challenging, given the high salt content of generally available foods.

Gupta noted that the study did use commercially available products in the low-sodium diets and the menus are available for people to follow, making it more accessible than some diets used in previous studies.

“What may also be attractive to people is that you don’t have to wait for months to see an effect. If you start to consume a low-sodium diet, you can see results on blood pressure rapidly, within a week,” he commented.

The diet in this study brought about a large reduction in dietary sodium, but Gupta says any reduction in dietary sodium is likely to be beneficial.

“If you go to the level that we got to, you could expect to see a reduction of around 6 mm Hg. But it’s like walking — you don’t necessarily need to get to 10,000 steps every day. Any amount of walking or physical activity is of benefit. The same is probably true for salt: Any reduction that you can make is probably of benefit.”

For the study, participants had their blood pressure measured by 24-hour ambulatory monitoring while on their usual diets. They were then randomly assigned to either a high-sodium diet or a low-sodium diet for 1 week. Participants then crossed over to the opposite diet for 1 week, with blood pressure measured over a 24-hour period on the last day of each diet.

As assessed by 24-hour urine excretion, the usual diet of participants was found to already be high in sodium (median, 4.45 g/d). This increased to a median of 5.00 g/d when on the high-sodium diet in the study and decreased to 1.27 g/d while on the low-sodium diet.

Results found participants had a median systolic blood pressure of 125mm Hg on their usual diets. This was raised to 126 mm Hg on the high-sodium diet and lowered to 119 mm Hg on the low-sodium diet.

The researchers also report that 75% of individuals showed a blood pressure reduction on the low-sodium diet and are thus defined as “salt-sensitive.” This is a higher percentage than found in previous studies.

“Of those that didn’t show a blood pressure reduction with a low-sodium diet in this study, it appears that they may not have been so adherent to the diet as those who did show a blood pressure reduction,” Gupta said.

He noted that hypertension is the most common chronic disease condition worldwide, with about 1.3 billion people affected, and although it has been known for some time that dietary sodium affects blood pressure, there have been some gaps in previous studies.

For example, many previous studies have excluded individuals who were already taking antihypertensive medications and people with diabetes, and they have generally not included many older individuals. The current study found that all of these groups also showed significant blood pressure reductions by reducing dietary sodium.

Large Effect in People With Diabetes

Subgroup analysis largely showed consistent results across the population, regardless of age, sex, race, and body mass index and whether participants were taking antihypertensive medication or not, but there were a couple of exceptions. Individuals with higher blood pressure at baseline seemed to have a greater effect of lowering dietary sodium, although those who were normotensive at baseline still showed significant blood pressure reduction, Gupta reported.

The researchers also found a particularly large reduction in blood pressure from lowering sodium intake in people with diabetes, who made up about 21% of the overall cohort. Their average reduction in systolic blood pressure between the high and low sodium diet was close to 17 mm Hg rather than the 7-8 mm Hg in the whole cohort.

Gupta said that the results are applicable to most of the population.

“The people who will be most motivated to follow a low-sodium diet are those with hypertension. But even in normotensive individuals, there is likely to be benefit.”

To help people follow a low-sodium diet, Gupta says education campaigns are needed “to show people that they can do it and make it work.” But there are bigger structural issues that need to be addressed at policy and governmental levels.

“Most of our food available in grocery stores and restaurants is high in salt. We now have a preponderance of evidence showing us that we need to change what’s available in the food supply,” he said. “There is a push going on for this now, and the US has introduced some guidelines for the food industry on sodium content of foods. These are voluntary at this point, but it’s a start.”

Difficult to Maintain Long-Term

Commenting for theheart.org | Medscape Cardiology, Paul Whelton, MD, chair in global public health at Tulane University School of Medicine, New Orleans, noted that sodium reduction is known to reduce blood pressure, with greater sodium reductions giving greater blood pressure decreases, and that some people are more sensitive to the effects of sodium than others.

He described CARDIA-SSBP as a “well-done study.”

“They managed to get a very low sodium intake and a large difference between the two groups, which translated into a big reduction in systolic blood pressure,” Whelton said. “However, the problem with these sorts of trials where the diets are provided to the participants is that although they show proof of concept, it is difficult to generalize because we can’t normally provide patients with their meals. In this type of ‘feeding’ study, we find it difficult to maintain people on their behavioral intervention over the long-term.”

Whelton said that he was more excited about this trial knowing that the food given was commercially available. “That makes it more practical, but you still have to be quite motivated to follow a diet like this. Buying low-sodium products in the supermarket does require quite a lot of work to read the labels, and sometimes the low-sodium foods are specialty products and are more expensive.”

He pointed out that older people in higher socioeconomic classes are more likely to attempt this and do better from behavioral interventions in general. “Unfortunately, people who don’t do well from behavioral interventions like this are those from lower socioeconomic groups, who are ones at most at risk for cardiovascular disease.”

Whelton noted that the food industry has been reluctant to lower sodium content because high-salt foods sell better. “Unfortunately, foods high in saturated fat and salt taste good to most people. We are generally attuned to a high salt intake. But when people have been following a low-salt diet for a while, they generally don’t like high-salt foods anymore. They become attuned to lower-sodium diet,” he added.

New US Sodium Reduction Guidelines

Discussant of the CARDIA-SSBP study at the AHA meeting, Cheryl Anderson, MD, University of California, San Diego, said that the findings were important and consistent with prior studies.

“These studies have global implications because salt is ubiquitous in the food supply in much of the world,” she noted, adding that, “Americans consume almost 50% more sodium than recommended, and there has been a persistent lack of adherence to healthy diet recommendations for reductions in salt, sugar, and fats.”

Anderson pointed out that in 2021, the US Food and Drug Administration issued guidance for voluntary sodium reduction, which uses a gradual approach, with targets to reach a population goal of 3000 mg/d of sodium by 2023 and 2300 mg/d by 2031.

“These targets apply to 150 categories of food that are sales-weighted to focus on dominant sellers in each category. They apply to food manufacturers, restaurants and food service operations,” she concluded. “These targets serve as a basis for continued dialogue. The research community eagerly awaits the review of population-based data to help refine this approach and goals.”

This study was supported by grants from the National Heart, Lung, and Blood Institute (NHLBI), the National Institutes of Health, the American Heart Association, and the National Center for Advancing Translational Sciences. The authors report no disclosures.

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